Preform assembly, container assembly, and method of manufacture

ABSTRACT

A method of making a preform assembly including providing a finish ring of plastic construction, placing the finish ring onto a core pin, introducing a preform polymer into a mold cavity that includes the core pin, and compression molding the preform polymer to the finish ring. A resulting preform assembly, and container assembly blow-molded from the preform assembly, are also disclosed.

The present invention is directed to preform assemblies for blow moldingplastic container assemblies, to plastic container assemblies blowmolded from such preform assemblies, and to methods of making suchpreform assemblies and container assemblies.

BACKGROUND AND SUMMARY OF THE INVENTION

In the manufacture of plastic containers, it is conventional toinjection mold or compression mold a container preform having a body anda neck finish with one or more external threads or other closureattachment means. The preform neck finish typically is molded to itsfinal geometry, while the body of the preform subsequently is blowmolded to the desired geometry of the container body. The preform may beof monolayer construction, or may be of multilayer construction in whichone or more intermediate layers in the preform body may or may notextend into the neck finish of the preform. U.S. Pat. Nos. 4,609,516,4,710,118 and 4,954,376 illustrate injection molding of multilayercontainer preforms.

Molding the neck finish portion of a container as part of the containerpreform presents a number of problems. For example, when the preformsare formed by injection molding, the plastic material typically isinjected into a mold cavity at the closed end of the preform body, sothat the material must flow along the sides of the preform mold cavityinto the area in which the neck finish is molded. The neck finishtypically requires more accurate and stable dimensioning than the bodyof the preform, which can limit the cycle time of the preform moldingprocess. Furthermore, the neck finish of the preform is of the samematerial as a monolayer preform body, and of the same material as atleast the outer layers of a multilayer preform body, which limits theability to obtain the most desirable material characteristics at theneck finish. When the preform is of polyester construction, such aspolyethylene terephthalate (PET), the neck finish of the preform can bewholly or partially crystallized to improve the operatingcharacteristics of the neck finish area, particularly in hot-fillcontainer applications. However, the requirement that the neck finish beof the same material as at least the outer layers of a multilayerpreform body still limits the design capabilities of preformmanufacture.

A method of making a preform assembly in accordance with one aspect ofth present invention includes providing a finish ring of plasticconstruction, placing the finish ring onto a core pin, introducing apreform polymer into a mold cavity that includes the core pin, andcompression molding the preform polymer to the finish ring.

In accordance with a second aspect of the present invention, there isprovided a preform assembly for blow molding a container assembly, whichincludes a molded plastic finish ring and a plastic preform compressionmolded to the finish ring such that a neck portion of the plasticpreform radially interengages the finish ring.

In accordance with a third aspect of the invention, there is provided acontainer assembly blow molded from a preform assembly which is producedfrom compression molding a preform to a molded plastic finish ring. Thecontainer assembly includes the molded plastic finish ring, and aplastic container having a neck portion thereof radially interengagingsaid finish ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objects, features, advantagesand aspects thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings, inwhich:

FIG. 1 illustrates a side elevational view of a preform assemblyaccording to one exemplary embodiment of the present invention;

FIG. 2 illustrates a side elevational view of a container assembly,blow-molded from the preform assembly of FIG. 1, according to anotherexemplary embodiment of the present invention;

FIG. 3 illustrates a side elevational view of a finish ring for thepreform and container assemblies of FIGS. 1 and 2;

FIG. 4 illustrates a top view of the finish ring of FIG. 3;

FIG. 5 illustrates a cross-sectional view of the finish ring of FIG. 3,taken along line 5-5;

FIG. 6A illustrates a compression molding apparatus for use inaccordance with an exemplary method of the present invention, whereinthe apparatus is shown in an open position in which a charge of preformmaterial is located within a mold cavity and a pre-made finish ring isloaded to a core pin;

FIG. 6B illustrates the compression molding apparatus of FIG. 6A whereinthe apparatus is shown in a closed position in which the preformmaterial is compression molded within a portion of the pre-made finishring;

FIG. 7 illustrates a fragmentary cross-sectional view of a portion ofthe compression molding apparatus of FIGS. 6A and 6B and across-sectional view of the resulting preform assembly, wherein thepreform assembly has been retracted and is carried on the compressioncore pin; and

FIG. 8 illustrates an enlarged cross-sectional view of the preformassembly of FIG. 7, taken from circle 8 thereof.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a preform assembly 20 in accordance with onepresently preferred embodiment of the invention as comprising a preform22 and a separate finish ring 24 secured thereover. The preform 22 maybe injection molded, but is preferably produced by compression moldingas will be discussed in greater detail below. The preform 22 is composedof any suitable plastic material such as monolayer polyethyleneterephthalate (PET) or the like, or multilayer PET or the like in whichmatrix layers of PET, for example, alternated with one or more layers ofa barrier resin material such as ethylene vinyl alcohol (EVOH), nylon orthe like. The finish ring 24 is injection or compression molded or thelike, and is composed of any desired material such as PET, post consumerresin (PCR), process regrind (REG), polypropylene (PP), polyethylene(PE), polyethylene napthalate (PEN), or the like. Preferably, however,the finish ring 24 is composed of a material different than that of thepreform 22, such as amorphous PET for preform 72 and crystalized PET forfinish ring 24. FIG. 2 illustrates a container assembly 120 that is blowmolded from the preform assembly 20 of FIG. 1 in accordance with anotherpresently preferred embodiment of the present invention, and includesthe finish ring 24 secured to a container 122 in a manner that is in allsignificant respects identical to that of the preform assembly 20 fromwhich the container assembly 120 is blow-molded. Accordingly, suchsecurement details will not be repeated for this embodiment.

In FIG. 1, the preform 22 includes a closed lower end 26 and extendsupwardly therefrom in the form of a body 28 that terminates in acylindrical neck 30 that is integrally molded with the body 26.(Directional words such as “upper” and “lower” are employed by way ofdescription and not limitation with respect to the upright orientationof the preform assemblies and components illustrated in the drawings.Directional words such as “radial” and “circumferential” are employed byway of description and not limitation with respect to the axis of thepreform neck or finish ring as appropriate.) As also shown in FIGS. 3-5,the finish ring 24 is circumferentially continuous and includes anannular cylindrical wall 32 having one or more external threads orthread segments 34. In the preferred embodiment illustrated in thedrawings, a circumferential bead 36 extends around the outer surface ofthe wall 32 beneath the threads 34 for cooperating with atamper-indicating mechanism on a closure (not shown) to be secured tothe finish portion of the final container. A capping or support flange38 extends radially outwardly from the lower end of the wall 32, givingthe finish ring 24 a generally L-shaped lateral cross section in theillustrated embodiments of the invention. As best shown in FIG. 5, thefinish ring 24 includes a cylindrical internal surface 40 and a taperedinternal surface 42 extending between top and bottom ends 44, 46.Annular grooves 48 are provided in the tapered internal surface 42, aswill be further described in reference to FIGS. 6A-8 below.

Referring now in general to FIGS. 6A-8, there is illustrated acompression molding apparatus 50 for use in accordance with an exemplarymethod of the present invention. In FIG. 6A, the apparatus 50 includes acore pin 52 positioned above a compression mold 54. The compression mold54 includes a closed bottom end 56, a body portion 58, and a partialfinish portion 60 that together define a mold cavity 62. The apparatus50 occupies an open position in FIG. 6A, in which a charge of preformmaterial 64 is introduced into the compression mold cavity 62 and thepre-made finish ring 24 is placed on to the compression core pin 52, asshown. The charge 64 is soft or molten, and thereby conforms to andfills the lower end of the mold cavity 62. The core pin 52, with thefinish ring 24 mounted thereto, and the mold 54 are positioned invertical alignment.

As shown in FIG. 6B, the core pin 52 and finish ring 24 are then movedinto the mold 54 to compression overmold the charge 64 partially withinthe finish ring 24. The term “overmold” is a term of art and, as usedherein, means to mold one component from a soft or molten state toanother component in a solid or finished state. The molten preformmaterial charge 64 flows in an upward or forward direction between thecore pin 52 and mold 54. As a result, the preform 22 is formed includingthe closed bottom end 26, the body 28 and the neck 30. Moresignificantly, however, the preform assembly 20 is formed from theovermolding of the preform 22 to the finish ring 24. Thereafter, and asshown in FIG. 7, the core pin 52 is retracted with the preform assembly20, including the preform 22 and finish ring 24, mounted thereto.

As shown in FIG. 8, the preform assembly 20 includes the preform 22compression molded partially within a portion of the finish ring 24.More specifically, the neck 30 of the preform 22 includes an upperportion 66 having annular projections 68 that extend into the annulargrooves 48 of the finish ring 24 so as to positively radially interlockor interengage the finish ring 24 to the preform 22. The annular grooves48 in the finish ring 24 can also be referred to as radial recesses orradial interengagement features. The radial interengagement between thepreform 22 and finish ring 24 provides positive resistance to anyaxially applied force tending to separate the components 22, 24. Thepreform 22 also includes a tapered or conical external surface 70 thatcorresponds to the tapered or conical internal surface 42 of the finishring 24. The tapered internal surface 42 of the finish ring 24 isgreater in diameter than the corresponding portion of the core pin 52.Accordingly, a small gap 72 is provided between the core pin 52, taperedinternal surface 42 of the finish ring 24, and a leading edge 74 of thepreform 22. In terms of the preform assembly 20, the gap 72 is providedbetween a transition point 76 of the finish ring 24 and the forward edge74 of the preform 22, wherein the transition point 76 is defined by theintersection of the cylindrical or straight internal surface 40 and thetapered internal surface 42. The gap 72 is intentionally provided toaccommodate within-tolerance variation of the size, volume or weight ofthe molten preform charge. In other words, at least some gap 72 shouldalways be present under maximum material conditions of both the preform22 and the finish ring 24, to ensure a proper fit therebetween withoutany distortion due to overpacking of the preform material into thefinish ring 24. The term “overpack” is a term of art and, as usedherein, refers to a condition where an excessive amount of moltenpolymer is compression molded and tends to lead to difficulties inejecting the finished formed part or parts from the compression moldingapparatus. Overpacking also tends to lead to warpage of, and residualstress within, the finished part or parts.

With one or more of the embodiments described above, the presentinvention provides a number of advantages. The present inventionfacilitates production of preform assemblies and container assemblieswherein a finish ring is composed of a material different from that of apreform or container to which the finish ring is radially interengaged.Likewise, the present invention facilitates application of finish ringsof various sizes and/or materials, to a common size preform and/orcontainer. Moreover, the present invention enables a decrease in thecycle time required to produce a preform because the constraint of theprocess—forming the neck finish portion—can be subordinated to aseparate, parallel production process for producing just finish rings.In the same vein, the present invention enables a reduction in the pieceprice of each preform because the mold tooling can be simplified, andreduced in cost, to omit the complex thread split features typicallyrequired for the threaded finish portion of the preform.

There have thus been described preform assemblies for blow moldingplastic container assemblies, plastic container assemblies blow moldedfrom such preform assemblies, and methods of making such preformassemblies and container assemblies that fully satisfy all of theobjects and aims previously set forth. The present invention has beendisclosed in conjunction with presently preferred embodiments thereof,and a number of modifications and variations have been discussed. Othermodifications and variations will readily suggest themselves to personsof ordinary skill in the art in view of the foregoing description.Indeed, the invention is intended to embrace all modifications andvariations as fall within the spirit and broad scope of the appendedclaims.

1. A method of making a preform assembly, said method including: (a)providing a finish ring of plastic construction, (b) placing said finishring onto a core pin, (c) introducing a preform polymer into a moldcavity, (d) placing said core pin and finish ring into said mold cavityaround said core pin, and (e) compression molding said preform polymerto said finish ring.
 2. The method of claim 1 wherein said step (a)includes providing said finish ring with an internal surface having atleast one radial interengagement feature, such that a portion of saidpreform polymer flows during said step (e) into interengagement withsaid at least one radial interengagement feature during said compressionmolding step.
 3. The method of claim 2 wherein said step (a) includessaid at least one radial interengagement feature being at least oneradial recess, such that a portion of said preform polymer flows intosaid at least one radial recess during said compression molding step. 4.The method of claim 3 wherein said step (a) also includes said at leastone radial recess being at least one annular groove, such that a portionof said preform polymer flows into said at least one annular grooveduring said compression molding step.
 5. The method of claim 1 whereinsaid step (a) includes providing said finish ring with an internalsurface having at least a portion thereof greater in diameter than saidcore pin, such that a gap is formed during said step (e) between said atleast a portion of said internal surface, said core pin, and a forwardedge of said preform polymer, said gap being provided to accommodatewithin-tolerance variation of a molten charge of said preform polymer toprevent overpacking of said preform polymer into said finish ring.
 6. Apreform assembly produced by the method of claim
 5. 7. A preformassembly produced by the method of claim
 1. 8. A method of making acontainer assembly includes blow molding the preform assembly of claim7.
 9. A container assembly produced by the method of claim
 8. 10. Apreform assembly for blow molding a container assembly, which includes:a molded plastic finish ring, and a plastic preform compression moldedto said finish ring such that a neck portion of said plastic preformradially interengages said finish ring.
 11. The preform assembly setforth in claim 10 wherein said finish ring includes at least oneinternal surface with at least one radial interengagement feature formedtherein, further wherein said neck portion of said plastic preformradially interengages with said at least one radial interengagementfeature.
 12. The preform assembly set forth in claim 10 wherein saidfinish ring includes at least one tapered internal surface, at least onestraight internal surface, and a transition point therebetween, andwherein there is an open gap between said transition point and a forwardedge of said neck portion of said plastic preform to prevent said neckportion of said plastic preform from being overpacked into said finishring.
 13. A container assembly blow molded from a preform assemblyproduced from compression molding a preform to a molded plastic finishring, said container assembly includes: said molded plastic finish ring,and a plastic container having a neck portion thereof interengaging saidfinish ring.
 14. The container assembly set forth in claim 13 whereinsaid finish ring includes at least one internal surface with at leastone radial interengagement feature formed therein, and wherein said neckportion of said plastic container interengages with said at least oneradial interengagement feature.
 15. The container assembly set forth inclaim 14 wherein said finish ring includes at least one tapered internalsurface, at least one straight internal surface, and a transition pointtherebetween, and wherein a gap is defined between said transition pointand a forward edge of said neck portion of said plastic container toprevent said neck portion of said plastic container from beingoverpacked into said finish ring.